MRI-CGCM模式气候预测回报试验在东亚夏季的检验和降尺度订正

Verification and correction of hindcast in summer over East Asia based on MRI Coupled Ocean-atmosphere General Circulation Model

中文关键词:  MRI-CGCM  东亚夏季风  中国东部夏季降水  降尺度  奇异值分解

英文关键词:MRI-CGCM  East Asian summer monsoon  Summer rainfall in East China  Downscaling  SVD

中文摘要:

      应用1979—2010年MRI-CGCM模式回报、NCEP/NCAR再分析数据和中国东部降水观测资料检验了模式对东亚夏季风的模拟能力，并利用模式500 hPa高度场回报资料建立了中国东部夏季降水的奇异值分解（SVD）降尺度模型。模式较好地模拟了亚洲季风区夏季降水的气候态，但模拟的季风环流偏弱、偏南，导致降水偏弱。模拟降水的方差明显偏小，且模拟降水的外部、内部方差比值低，模拟降水受模式初值影响较大。模式对长江雨型的模拟能力最高，华南雨型次之，华北雨型最低。模式对东亚夏季风第1模态的模拟能力明显高于第2模态。对于东亚夏季风第1模态，模式模拟出了西太平洋异常反气旋，但强度偏弱，且未模拟出中高纬度的日本海气旋、鄂霍次克海反气旋，导致长江中下游至日本南部降水偏弱。各时次模拟环流均能反映但低估了ENSO衰减、印度洋偏暖对西太平洋反气旋的增强作用。对于东亚夏季风第2模态，模式对西太平洋的“气旋-反气旋”结构有一定的模拟能力，但未模拟出贝加尔湖异常反气旋和东亚沿海异常气旋，导致中国东部“北少南多”雨型在模拟中完全遗漏。仅超前时间小于4个月的模拟降水能够反映ENSO发展对降水分布的作用。通过交叉检验选取左场时间系数可以提高降尺度模型的预测技巧，SVD降尺度模型在华南、江南、淮河、华北4个区域平均距平相关系数分别为0.20、0.23、0.18、0.02，明显高于模式直接输出。

英文摘要:

      Based on the hindcast data of MRI-CGCM of Japan Meteorological Agency, the NCEP/NCAR reanalysis data and precipitation observations in eastern China during 1979-2010, the ability of MRI-CGCM to simulate the East Asian summer monsoon (EASM) is examined. The SVD downscaling method for predicting summer rainfall in eastern China is proposed. The MRI-CGCM can reasonably reproduce the climatological summer rainfall in the Asian monsoon region. However, the simulated monsoon circulation is weaker than observations and shifts southward, which leads to underestimation of the simulated rainfall. The variance of simulated precipitation is smaller than that of observations and the ratio of its external to internal variance is lower than that of 500 hPa height, which indicates that the simulation is obviously affected by the initial condition. The simulation skill for the summer rainfall anomaly pattern over the Changjiang River valley is the highest, followed by that in South China, and the skill for simulation of North China anomaly pattern is the lowest. The model ability to simulate EOF1 of the EASM is considerably higher than that for the EOF2 simulation. The MRI-CGCM can well simulate the western North Pacific anticyclone, but underestimates its intensity. The model can reflect the effects of ENSO decaying and Indian Ocean warming on rainfall anomalies, but these effects are underestimated. For the EOF2 of EASM, the MRI-CGCM can to a certain degree realistically simulate the cyclone-anticyclone structure over the western Pacific. Only those simulations at a four-month leading time can partially reflect ENSO developing effects on rainfall. Choosing the time coefficients of the 500 hPa-heights modes through cross-validation can improve the prediction skill. The average ACCs of the SVD downscaling method are 0.20, 0.23, 0.18, and 0.02 over South China, Jiangnan, Huaihe and North China, respectively, which are significantly higher than that from the hindcast.